VEIL Solutions MagBlock Safety Mag Block insert for AR/M4 style rifles designed to be used in dry practice for training environments, CQB training, or as a safety block for competitions that require chamber flags / safety flags. Will hold bolt to the rear. "CLEAR" writing visible with port door open - does NOT force port door open. Safety Orange color. If you are ordering for a MIL/LEO unit, please visit our GOVERNMENT SALES page for further info.